Enhanced service life bolt

ABSTRACT

A firearm having a stock and barrel attached to a receiver. Located within the receiver is an enhanced service life bolt. The enhanced service life bolt has a plurality of lugs. At least one lug has a reduced height that is shorter than the height of the other lugs. The enhanced service life bolt defines an extractor slot and the at least one reduced height lug is located adjacent to the extractor slot. The at least one reduced height lug is approximately twenty percent (20%) shorter than the other lugs. The enhanced service life bolt is constructed from a maraging stainless steel, such as 158 Carpenter Stainless Steel.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/380,806, filed Sep. 8, 2010, entitled “ENHANCED SERVICE LIFE BOLT”,the aforementioned application being hereby incorporated by reference inits entirety.

FIELD OF THE INVENTION

The present invention relates generally to firearms and, moreparticularly, to an improved bolt design for a firearm which enhancesthe service life of the bolt.

BACKGROUND OF THE INVENTION

Many service firearms, such as the M4/M16 family of rifles, as discussedby Duncan Long in The AR-15/M16 A Practical Guide, Paladin Press, 1985incorporated in its entirety by reference, employ ammunition thatgenerates high bullet energies and velocities. An example of suchammunition is the 5.56×45 mm NATO or “M855” cartridge. Such cartridgesgenerate relatively high temperatures and pressures within the firearmduring use. The M4/M16 family of rifles typically employs a gas-operatedbolt assembly that includes a multi-lug bolt and a barrel extension withwhich the bolt locks and unlocks in firing each round of ammunition. Thebolt assembly also includes an elongated firing pin, a spring-loadedejector and a spring-loaded extractor configured to releasably engage acartridge as it is placed in the firing chamber.

When each round of ammunition is fired, the interlocked bolt receives aforce that is transmitted from the face of the bolt to its lugs which,in turn, transmit the force to the corresponding lugs of the barrelextension. In particular, during discharge of ammunition a bendingmoment is exerted upon the bolt lugs when the bolt lugs engage the lugsof the barrel extension.

One potential issue resulting from the combination of temperatures andpressures generated during firing is an increase in wear of the bolt,and particularly an increase in wear of the bolt lugs. As a result ofthis increase in wear comes the possibility of reduced bolt life. Knownbolt designs for the M4/M16 family of rifles typically have a servicelife of around 6,000-8,000 rounds, after which time the bolt must bereplaced.

Accordingly, it is desirable to increase the bolt life of such firearmsas much as practicable. More specifically, it is desirable to increasethe bolt life of a firearm to beyond 13,000 rounds.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention toprovide a bolt for a firearm having an enhanced life.

It is another object of the present invention to provide a firearmhaving a stock, a receiver, a barrel, and a bolt having an enhanced lifethrough the use of a stronger tensile strength material.

It is another object of the present invention to provide a bolt havingan enhanced life through the use of a material that is heat treated forimproved impact resistance.

It is yet another object of the present invention to provide a bolthaving an enhanced life through the use of at least one low profile boltlug located on both sides of the asymmetrical section of the bolt.

The present invention provides an enhanced life bolt for a firearm thatincludes the use of a maraging stainless steel, a heat treatment toprovide maximum impact resistance and at least one low profile lockinglug to reduce the bending moment of the lug most prone to wear toachieve a service life of the bolt in excess of that expected from knownbolt designs.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from reading thefollowing description of non-limiting embodiments, with reference to theattached drawings, wherein below:

FIG. 1 is an exploded perspective view of a prior art bolt design.

FIG. 2 is a rear view of the prior art bolt design of FIG. 1 showing thelugs on the bolt head.

FIG. 3 is a detailed perspective view of the prior art bolt design ofFIG. 1 showing the head thereof.

FIG. 4 is a rear view of an enhanced life bolt in accordance with oneembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a prior art bolt design for the M4/M16 family ofrifles is shown. The bolt 12 has a proximal end 14, a distal end 16terminating in bolt face 18 surrounded by an integral bolt head 20 andan integral cylindrical portion 22 disposed between the proximal end 14and the distal end 16 along a longitudinal axis or bolt centerline 24.The bolt 12 also has a longitudinal opening 26 in the integralcylindrical portion 22 to receive an extractor 28.

As shown in FIG. 2, the bolt head 20 has a plurality of bolt lugs 30with walls 32 extending integrally and radially outward therefrom. Thisprior art bolt design employs seven (7) lugs 30 to lock the bolt withthe barrel extension during the firing of each round of ammunition. Eachlocking lug 30 is symmetrical and is substantially the same in terms ofdimensional specifications. In addition, as further shown in FIG. 2,each locking lug is spaced the same distance, and extends outward thesame distance, from the bolt centerline 24. With the prior art boltshown in FIG. 2, each of the lugs 30 has the same height, h1, or 0.1065″for the current M4/M16 family. Known M4/M16 bolts are often manufacturedusing 158 Carpenter Stainless Steel.

As stated above, the forces and temperatures generated during the firingof ammunition increases wear of the bolt 12, and in particular the boltlugs 30. The wear of the bolt 12 mandates replacement of known bolts ataround 6,000-8,000 rounds. As shown in FIG. 3, wear is often mostprominent around either of the locking lugs 30 straddling the extractorslot 26. These areas of wear are designated by arrow, W.

Turning now to FIG. 4, the enhanced life bolt 50 of the presentinvention is shown. The bolt has substantially the same configuration asthe prior art bolt design described above and shown in FIGS. 1-3, with anotable exception being the configuration of the bolt head and lockinglugs. The enhanced life bolt 50 of the present invention is alsomanufactured from a stronger tensile strength material than that usedfor known bolts for the M4/M16 family of rifles that is heat treated forimproved impact resistance. Preferably, a maraging stainless steel, suchas Carpenter 465 Stainless Steel is used, although other materialsexhibiting strong tensile strength and improved impact resistance over158 Carpenter Stainless Steel can be used.

The bolt 50 includes two locking lugs 52 straddling an extractor slot54, which are reduced in height as compared to the other lugs 56. In thepreferred embodiment, the full height lugs 56 have a height h1 while thetwo locking lugs straddling the extractor slot have a height h2 that isless than h1. As shown, h1 is about 0.1065″. Preferably, h2 is about0.0850″, or 0.0215″ (approximately 20%) less than h1. Other heightconfigurations and relationships are also possible provided that the twolocking lugs 52 straddling the extractor slot 54 are reduced in heightas compared to the other lugs 56. This reduction in height differs fromprior art bolt 12, as shown in FIGS. 1-3. The prior art bolt 12 hasseven (7) equally sized lugs and the presently disclosed bolt 50 hasfive (5) lugs 56, sized substantially equivalently to the lugs of theprior art bolt 12, and two (2) low-profile lugs 52. The inclusion of thetwo low-profile lugs 52 eliminates the high contact point withoutsacrificing strength, which has been validated through finite analysisand physical testing.

The approximate 20% reduction in height reduces the bending moment onthese two low-profile lugs. This reduction plus the changes made inmaterial properties increase the service life of the bolt from6,000-8,000 rounds to in excess of 13,000 rounds. In addition, thelocking area is reduced approximately 10% from the prior art design. Thereduction is offset by the improved tensile strength of the material.

Although this invention has been shown and described with respect to thedetailed embodiments thereof, it will be understood by those of skill inthe art that various changes may be made and equivalents may besubstituted for elements thereof without departing from the scope of theinvention. In addition, modifications may be made to adapt a particularsituation or material to the teachings of the invention withoutdeparting from the essential scope thereof. Therefore, it is intendedthat the invention not be limited to the particular embodimentsdisclosed in the above detailed description, but that the invention willinclude all embodiments falling within the scope of this disclosure.

What is claimed is:
 1. A firearm comprising: a stock; a receiverconnected with the stock; a barrel connected with the receiver; and anenhanced service life bolt located within the receiver; the enhancedservice life bolt having a plurality of lugs, at least one lug having areduced height being less than a height of another of the lugs.
 2. Thefirearm of claim 1, wherein the enhanced service life bolt defines anextractor slot, the at least one lug having a reduced height beinglocated adjacent to the extractor slot.
 3. The firearm of claim 1,wherein the at least one lug having a reduced height being approximatelytwenty percent (20%) shorter than the height of another of the lugs. 4.The firearm of claim 1, wherein the enhanced service life bolt beingconstructed from a maraging stainless steel.
 5. The firearm of claim 4,wherein the maraging stainless steel being Carpenter 465 StainlessSteel.
 6. The firearm of claim 4, wherein the maraging stainless steelbeing heat treated to improve impact resistance.
 7. An enhanced servicelife bolt comprising: a cylindrical portion; and a plurality of lugsextending radially outward along a distal end of the cylindricalportion, at least one lug having a reduced height being less than aheight of another of the lugs.
 8. The enhanced service life bolt ofclaim 7, wherein the at least one lug having a reduced height beingapproximately twenty percent (20%) shorter than the height of another ofthe lugs.
 9. The enhanced service life bolt of claim 7, wherein theenhanced service life bolt defines an extractor slot, the at least onelug having a reduced height being located adjacent to the extractorslot.
 10. The enhanced service life bolt of claim 7, wherein theenhanced service life bolt being constructed from a maraging stainlesssteel.
 11. The enhanced service life bolt of claim 10, wherein themaraging stainless steel being Carpenter 465 Stainless Steel.
 12. Theenhanced service life bolt of claim 10, wherein the maraging stainlesssteel being heat treated to improve impact resistance.
 13. A bolt headfor a enhanced service life bolt, the bolt head comprising a pluralityof lugs extending radially outward about a bolt face, two of theplurality of lugs being reduced height lugs, the bolt head defining anextractor slot, the reduced height lugs being positioned adjacent toeach side of the extractor slot.
 14. The bolt head of claim 13, whereinthe reduced height lugs having a reduced height being approximatelytwenty percent (20%) shorter than a height of the other lugs.
 15. Thebolt head of claim 13, wherein each of the reduced height lugs provide areduced bending moment during firing of ammunition being less than thebending moment of the other lugs.
 16. The bolt head of claim 13, whereinthe bolt head being constructed from a maraging stainless steel.
 17. Thebolt head of claim 16, wherein the maraging stainless steel beingCarpenter 465 Stainless Steel.
 18. The bolt head of claim 16, whereinthe maraging stainless steel being heat treated to improve impactresistance.